Makaziwe Mandela said the 94-year-old statesman's medical condition is beyond their control.

“I re-iterate that Tata (father) is very critical that anything is imminent,” she said as the Mandela family gathered at the Mediclinic Heart Hospital to visit the peace icon who has been admitted since June 8 for a recurring lung ailment.

“But I want to emphasise again that it's only God who knows when the time to go is and so we will wait with him, with Tata, as long for us as a family, he's still giving us hope opening his eyes he's still reactive to touch we will live with that hope until the final end comes,” she told media outside the hospital in Pretoria.

Mandela, whose health condition appears to have suddenly and dramatically deteriorated in recent days, today forced Zuma to cancel his trip to Mozambique, where he was to attend the key summit of Southern African Development Community.

Presidential spokesperson Mac Maharaj said Mandela's condition has worsened over the past 48 hours. However, doctors have assured Zuma that “they are still doing everything they can to ensure Mandela's wellbeing”, Maharaj said.

Mandela had a long history of lung problems, dating back to the time when he was a political prisoner on Robben Island during apartheid.

While in jail he contracted tuberculosis. Mandela is revered for leading the fight against white minority rule in the African country and then preaching reconciliation despite being imprisoned for 27 years.

Mandela, regarded the founding father of South Africa's multiracial democracy, served as the country's first black president from 1994 to 1999.

He left power after five years as president.

Mandela was awarded the Nobel Peace Prize in 1993. He retired from public life in 2004 and has rarely been seen at official events since.